Thermionic tube structure



M V'. 2 N. m .AM/,f4 F W H M9 .26 m W i 4 N y go, ,f i m N. B. KRIM Filed Jan. 19, 1946 THERMIONIC TUBE STRUCTURE oct. 26, 194s.

Patented Oct. 26, 1948 THERMIONIC TUBE STRUCTURE Norman B. Krim, Newton Highlands, Mass., as-

signor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application January 19, 1946, Serial No. 642,404

voltage, and that if the phase relations are corl rect, this induced grid voltage may add to the impressed alternating voltage in such a manner as to cause the amplifier to oscillate, which is undesirable. In the past, in order to reduce this grid-plate capacitance, a screen grid has been interposed to shield the grid from the plate, and

the control-grid terminal has been placed at the top of the tube, instead of on the base. However, in a tube of the sub-miniature type it is impracticable to place the control-grid terminal at the top of the tube, and, even though a screen grid is used to shield the elements themselves inside the tube, an objectionable capacitance exists between the grid and plate leads due to the fact thatthey pass parallel and very close to each other through the glass seal into the tube envelope.

An object of this invention is reduction of the capacitance which exists between the grid and plate leads cf a thermionic tube.

Another object is to devise an inexpensive means for reducing the capacitance existing between the grid and plate leads of a thermionic tube of the sub-miniature type, which is the type particularly adapted for use in hearing aids or pocket radio receivers.

A further object is to devise a tube structure which is capable of use at very high frequencies.

The foregoing and other objects of the invention will be best understood from the following description of some exemplications thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a longitudinal cross-section through a tube of the invention but with the tube elements shown in elevation;

Fig. 2 is a fragmentary View of a tube, similar to Fig. 1 but showing a modified construction; and

f Fig. 3 is a fragmentary side view of the tube taken along line 3-3 of Fig. 1.

Referring to the drawing and more particularly to Fig. 1 thereof, there is shown a thermionic tube of the sub-miniature type. The tube electrode assembly, generally indicated at I, is sealed inside an envelope 2 of some suitable material, such as glass. Upper and lower mica spacers-3 (Cl. Z50-27.5)

and 4, respectively, which engage the inside walls of the envelope at their peripheries, serve as spacing and insulating supports for the elements of the tube. Side support rods 5 and 6 are rmly attached to spacers 3 and 4 by means of clips 1 and in turn serve as grid supports for the wire 8 of the outermost or number three grid, which wire is wound in helical fashion on. rods 5 and 6 between the two spacers. Wire 9 of the intermediate or number two grid is similarly wound in helical fashion on similar support rods I0 and I I which are also attached to the spacers 3 and 4. Wire I2 of the innermost or control or number one grid is wound helically on side support rods I3 and i4, which are attached rmly to spacers 3 and 4 and which extend some distance below the lower spacer 4, as do also support rods 5, 6, I0 and II.

A pair of flat anode plates I5 are positioned on opposite sides of the flat portions of the grids, each being mounted upon a U-shaped frame I6 made of some suitable material, such as nickel wire. The llat portion of each of these frames engages the top of insulating spacer 3, depending side arms I'I and I8 thereof extending through holes in spacers 3 and 4, below the bottom spacer 4, and having plates I5 welded thereto between spacers 3 and 4. In order to electrically connect and securely fasten in place the two anode plates I5, a double-armed bracket (not shown), which engages the lower side of spacer 4, is welded to the lower ends of each of the side arms I'I.

The lament I9 is supported between a conducting spring member 20 at its upper end and a bracket 2l at its lower end, the bracket being fixed to insulating plate 4 by means of rivets 22. The spring member 20 is welded at one end to the upper end of the lamentary cathode I9 and at its other end to side rod 5. The lower end of the lament I9 is welded to bracket 2 I. A support 23 containing a number of cups for getter material may be conveniently supported on the electrode assembly by being welded to the upper end of side rod E.

A plurality of lead-in conductors are provided for the electrodes, all of the lead-ins being sealed through a lower at press 24 formed externally on envelope 2 to provide external electrical connections to the various electrodes. It will be apparent to those skilled in the art that, due to the parallel position and extremely close spacing of the lead-in conductors or wires for the control grid and plate, an objectionable amount of capacitance will exist between these two leadins, and the object of this invention is to reduce this capacitance. To accomplish this result, plate lead-in 25, which inside the envelope is welded to side arm l1 and is therefore electrically connected to plates I5, is surrounded over a portion of the length thereof by a hollow metallic tube 2S which is maintained at ground potential and which, in effect, electrostatically shields lead-inf 25rironli the Tother lead-inst *fTubeZ 6l surrounds conducto 25 through the entire length of the at press 2d and also a substantial distance above and below said press. Control grid lead-in 21, which at its upper end insi'd'e'the'errvelopev` is spot-welded to rod Ill and is therefore electrically connected to control grid l2; isf similarly.: ysurrounded or shielded by a hollowrnetallic tub'el28, which surrounds lead-in 21 entirely through the length of the press 2d and'.some"little-distance above and below the same and which is also grounded. In order to conveniently provide leadins 25 and 21 with their respective shields 25 and """zs, a short section of eoaxiaifiineis-usee forme if plate lead-in 25126, and another" shortsection .of.\coaXia1.linefor the "grid lead-in 212228.5 In .order to increase the mechanicals'tren'gth of the .sectionsof coaxialline, so that the'outer' conductors .will` not vbe crushed. when. the press is .produced,. a',l fller29oi-low loss material, for Y v...example polystyrene, is provided in, each section oicoaxialllineto entirely fill-upthespace inside .,...the outerhollow tubeswhich is not occupied by the ,finnerwres'Z or `2.1 respectively.l yIn order ...,toprovide. an airtight seal between they inner-.and fr youter conductors oteach section of coaxial line, a ,.globule oi-glass 3..is ,provided inthe innerv end Vv.-.off each` sectionl of coaxialline and is melted in 'position to eiectively :seal the-.space between the inner and outer conductors'of each section." Wire 3 I` is Welded to the intermediategrid support rod .LL to lservev as` theJead-in conductor for Athis grid, z andthis wire, along` with the sections.. of coaxial :line-.25-'f26- and 21.-28;are sealed.through...the ,s ...press in: the usual way. tof provide lead-ins. .for fheelectrod-es of thevtube.Vv ILead:32-=isvvelded at .none-rendite ,rod S-andfatzits other end-.toouter .conductoiw-Zof..coaxia1-.line 25.--25 to provide .:e1ectrical kconnection ,to the;1-upper. end. of v.the .flament.. .ILeadB is welded'at onelend to `bracket .5 21.-v and is sealed f throughs press/211iy yto lserveW as a rfflead-in toi. the: .lower fend ofl the-x lamentary cathode.

Thezembodiment ofy Fig. Zidiff'ers fromlthat of A :f-'Eig; lonly finthatwthe, grounded shieldsfor the :f outer conductors :ofthefcoaXialf-line sections of he-'l'control grid and plate lead-ins; are not solid metallic tubes; butare conductors'fwoveno metalr.: lic'strandsr into ai hollow-'cylindrical-configurafntion.; Iii-'order` to produce" such .coaxiall :linesections','1an1annulus Voifglass ,is `:molde-dvonto 'each ofrthe. inner'tconductors': 125:-4 and 21tr. and'then a hriaidedfsmeta'llic coveringf 34"01; '-35'1is/woven on hisiglass cylindri'calzbase; using afbraiding maif chine." .I Caps; con'si'stingvotrrrietalf:bands-35' :and 31, are fastened to opposite ends offfbra'iding 34 Tato prevent unraveling ofthe braidingywhile caps 38 and 39 are fastened to oppositefendsfoi braid- .l .ingl 3'5for'the' same' purpose." Leads '32x-and? 33 *vare'welded to caps 311and gwe'spe'ctively; to provide electrical connections between :fthe-'outer *conductors of the fcoaxial lines yand thelfopposite, ends of the filament, as ins-Fig'. 1.3' -IIe-rea1so,f.the ycoaxial sections extend entirely vthro'ughiiat press y* 24 and a substantial distancel abovef'and'below *the-same. When fthelglasso envelope-Eis heated, preparatory to formationA ''o'f the flat 'pressI by 'thelinner cylindersof :glasswon` which the braided outer"conduct`ors` are woven. In Fig. 2,

the same electrical connections are provided as in Fig. 1, and lead-ins 3|, 25-34, and 21-35 are Pall'sealedfinto press 24. In Fig. 2, the grounded braidings 3A and 35 have the same eiect as the "tube'sZGand ofFig. l; that is, they eiectively "shield the gridahd plate lead-ins from each other,

thereby reducing the capacitance between these ftwo 1 lead-ins.

`The outer conductors of the coaxial lines in both embodiments shown should be made of a metal which will seal in a vacuum-tight manner *with yglassfsothat such aseal can-be --achieved `around *therperiph'eries of Vthe outer conductors of the coaxial'flines.- Irr-Fig; 1,forf-exarnplefthe vvvsolid-outer tube should-be made'l ofV a=inaterial "woven conductor of Fig. 2 should be made'of a such as Vcopper or'chrome iron,-while*theouter V`material such as copper, dumet,-or tungsten.

` 'O-f'course; it is to be understood-that'thisiinvention is not limited to the particular-details as'described above, as many equivalents will suggest themselves to thoseskilled lintheart. *For example, for tubes'adaptedforuse'at' very high I frequencies, in'systems using coaxial lines: as lconductors of high-frequency" currents; a tube 'utilizing' this invention can' be inserted Adirectly into the coaxial line; utilizing coaxial'. lines ior grid and plate lead-ins in' accordance "withthe :"te'achings of. this i11venti'on,'but`y placing thetwo .coaxiallead-ins of the' invention .in opposite ends of the tube. Also, theinve'ntion may' be'u'sed in 'connection .withjtypes of envelopes :other Vthan 'i' 'thatfshowrr' such. 'as' iiat press receiving, tubes, ""acorn tubes, tubes 'having afbutton stem","etc.

It'isalso possible to eliminate the strengthening .filler in the coaxialline sections. .Although :the

inventionhas been described with reference to a pentode, it willl be obvious that it is Y.equally applicablelto a triode or 4to atubev having any vnumberof elements, as dong asY it has a control grid and an. anode or plate.' Various'other varialtionswill suggestthenis'elves. rIt is..acco`rdiiig1y desired that the appended claims .be given abroad interpretation commensurate with. thescope of -`this invention within.. the art.

What is..- claimed` is:

1. Means .for-y reducing the totalgrid-.elementvto-.plate-element capacitance-'of a Aktherrnonic .tube in a= sealed.envelopecomprising .twotmetallic shields,` one of said. .shields surrounding a-portion of the lead-in wire of one of said elementsy-the `other ofr-said..shields surrounding a portion of lthe" lead-inwire-fof =vthe--otherf of vsaid elements,

each of said portions being-thei-part'oi-{thefre- .'spectivey .lead-in wire which f-.passes .-th'rough the seal,v into .-saidfrenvelope. f

` 2. A thermionic tube comprising a grid, apath- .ode `onfoneside Aof...said grid, `a vplate.onr-the:oppo

siteside of said Agrid,A and-means forreducng the total grid-plate capacitance of saidtubey said Ymeans .consisting of a pair of metallic'..`shi`elds, one

"`of"'which 'surrounds the lead-inconductorlfor '-the grid and the other of whichsurroun'dsthe f lead-in conductor for t-he plate.

3.- A thermionicftube structure* comprising a. Lsealed envelope,v cathode, -gridy and plateeleme'nts mounted inside said envelope, and leadin conductors for each of said elements .passing through a sealing portion into said envelope, the lead-in conductors for the grid and plate elements each comprising a section of coaxial line which passes through said portion and is sealed thereinto.

4. Lead-in conductor structure for the grid and plate elements cf a thermionic tube in a sealed envelope, which comprises a press element at one end of said envelope and a pair of spaced coaxial lines sealed through said 4press element into the interior of said envelope, the inner conductor of one line being connected to said grid element and the inner conductor of the other line being connected to said plate element.

5. Lead-in conductor structure 'for the grid and plate elements of a thermionic tube in a sealed envelope, which comprises a press element at one end of said envelope and a pair of spaced coaxial lines sealed through said press element into the interior of said envelope, each of the coaxial lines consisting of an outer hollow metallic tube, an inner metallic conductor mounted therein, and a filler of low loss material occupying the remainder of the space inside the outer tube, the inner conductor of one line being connected to said grid elem-ent and the inner conductor of the other line being connected to said plate element.

6. Lead-in conductor structure for the grid and plate elements of a thermionic tube in a sealed envelope, which comprises a press element at one end of said envelope and a pair of spaced coaxial lines sealed through said press element into the interior of said envelope, each of the coaxial lines consisting of an outer conductor woven of metallic strands, an inner metallic conductor mounted therein, and a ller of plastic material occupying the remainder of the space inside the outer tube and filling the spaces between said strands, the inner conductor of one line being connected to said grid. element and the inner conductor of the other line being connected to said plate element.

NORMAN B. KRIM.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,647,238 Manthorne Nov. 1, 1927 2,281,041 Labin Apr. 28, 1942 

